This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2000-209861, filed Jul. 11, 2000, the entire contents of which are incorporated herein by reference.
The present invention relates to the structure of interconnections in digital semiconductor circuits and more specifically to the structure of power and ground lines in semiconductor devices or semiconductor integrated circuit chips adapted for high-frequency operation.
In digital semiconductor circuits, transistors act as on-off switches. Even if transistors are turned on, they cannot output any signal unless they are supplied with electrical energy. The transistors are connected to a power supply from which electrical energy is supplied and ground to which the supplied energy drains. If, when a switch, consisting of a transistor, is turned on quickly, its on resistance is low, then a phenomenon will occur in which, in supplying electrical energy (charges) from the power supply to the transistor, the power line shows a deficiency in charge supply capacity.
Why the power line fails to supply electrical energy will be described later in detail. Here, let us consider a power and ground line pair as a transmission line. If its characteristic impedance is, say, 50 ohms and the on resistance of the transistor is, say, 15 ohms, the power line will fail to supply electrical energy. Fortunately, in many cases, the characteristic impedance of the signal line connected to the transistor is higher than 50 ohms and the problem of shortage of electrical energy can be avoided; otherwise, it is required to lower the characteristic impedance of the power and ground line pair.
Another problem is the behavior of inductance of lines that resist an abrupt increase in current. Even if the characteristic impedance of the power and ground line pair is made lower than that of the signal line, when the transistor is turned on quickly, the parasitic inductance associated with the power and ground lines retards the supply of electrical energy through the power and ground lines. Therefore, it also becomes necessary to reduce the parasitic inductance associated with the power and ground lines.
Still another problem is that a signal may not be output at a sufficient level until the gate capacitance associated with the gate electrode has been fully charged. In other words, a problem arises in that the potential of an output signal does not reach a desired level in a short time. This is the delay associated with the operation of the transistor itself, causing the supply current to continue to flow until the output signal potential reaches a predetermined level. The load impedance at this time is different from the characteristic impedance of the signal transmission line and, simply stated, the current becomes infinite. if the power and ground lines in a pair form a transmission line, reflected noise appears on the transmission line during such an interval.
With conventional semiconductor circuit devices, the situation where the charge supply capacity of the power and ground lines and the transistor characteristics result in failure to switch transistors smoothly becomes noticeable especially in digital circuits that operate in frequency bands of the order of GHz.
It is therefore an object of the present invention to provide a semiconductor circuit device which allows power-ground pair lines to have a sufficient charge supply capacity without being limited by the characteristics of transistor gate circuits.
According to the present invention, there is provided a semiconductor circuit device comprising: a transmission line composed of a power line and a ground line which have substantially the same thickness and are formed one above the other, the power line and the ground line are electrically separated each other; and an electronic circuit coupled with the transmission line to receive a supply voltage through the transmission line.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.